The present invention relates to an apparatus for studying the structure of materials by obtaining X-ray diffraction patterns. More specifically, it is directed towards a novel apparatus for obtaining X-ray diffraction patterns of powdered substances under various conditions of temperature and for continuously following structural changes in the material due to temperature variations.
Many camera apparatus have been designed and used in the past to produce crystallographic data on film using one of the standard diffraction procedures. In this connection, there is known the Debye-Scherrer type of camera in which the specimen of material to be studied is mounted for rotation at the center of a circular cassette in which photographic film is wrapped around the iner wall of the camera. A collimated X-ray beam is then passed through a hole in the film and directed towards the specimen of material which is being continuously rotated. The resulting diffracted X-rays fall upon the cylindrically shaped film as a series of concentric rings. This series of concentric rings is the planar representation of a series of conical surfaces of different opening angles. These conical surfaces are so arranged that they have a common vertex at the source point of the ray and their axis extends in the direction of the primary ray. The opening angle of the conical surface and the intensity of the scattered radiation relative to the resulting diffraction cone are a function of the structure of the specimen of material which produces the diffraction.
The powder method for testing the X-ray diffraction characteristics of various materials is an extremely useful qualitative tool in both physics and chemistry. In the prior art, finely powdered material which is to be studied is drawn into a hollow fiber having a very small internal diameter. The procedure employed for filling the fibers is necessarily of such nature that the material being analyzed is usually maintained at room temperature and exposed to the atmosphere during the filling operation. The material is also exposed to the atmosphere in most conventional diffraction studies during the time that it is subjected to X-rays. On the other hand, X-ray diffraction studies can also be carried out at extremely high temperatures when employing special types of apparatus, which are modifications of the Debye-Scherrer type of camera. It is, however, of considerable interest to be able to detect temporary structural changes uninterruptedly, and to discover changes in the materials which occur upon changes in temperature.
Although a number of variable temperature powder diffraction cameras are known in the prior art, each of these cameras is a modification or an improvement over the Debye-Scherrer geometry. A distinct disadvantage of the Debye-Scherrer type camera in conducting variable temperature studies is the relatively closed geometry of the camera. Cameras utilizing flat-plate recording techniques employ an open geometry and have proved useful for variable temperature studies of materials, particularly of the mesomorphic phase transitions of organic and organometallic compounds wherein only low-angle diffraction lines are observed.
It is, therefore, a primary object of this invention to provide a novel apparatus for conducting X-ray diffraction studies of powdered substances under various conditions of temperature.
It is another object of this invention to provide a continuously recorded diagram of structural changes in materials which occur upon changes in temperature.
It is further an object of this invention to provide a powder diffraction camera in which the setup procedures required to perform variable temperature studies may be conducted without removing the camera from the diffraction unit to which it is attached.
In carrying out these and other objects of the present invention there is disclosed a flat-plate powdered diffraction camera which is suitable for variable temperature studies of powdered materials. The camera of the present invention is mounted on a conventional powder camera track and up to five 1 inch pictures can be taken on each 5 by 7 inch Weissenburg film by moving filmholder to expose segments sequentially, thus presenting side-by-side comparison of structural changes observed during mesomorphic transition in various specimens of material. The filmholder is mounted asymmetrically with respect to the X-ray beam since the sample capillary is near the base of the camera and the film to be exposed is vertically mounted in back of it. Both positive and negative diffraction lines are recorded for low order reflections, and tan 2.theta. is recorded instead of the normal 2.theta. angle. Samples of materials to be studied are sealed in evacuated heat resistant glass capillaries and mounted in a rotatable spindle assembly. The axis of the X-ray beam is designed to intersect the longitudinal axis of the sample capillary at right-angles. The temperature of the sample capillary is accurately regulated by directing a temperature controlled air stream, which emanates form the spindle assembly, along the longitudinal axis of the sample.